Entourage 2004 has been released to manufacturing, so I can now talk about it. I've been working with it for the last several months, and it's a great piece of work. I'm working on a long article on it for Exchange & Outlook Administrator, but in the meantime, you might be able to try it for free. What? It's true. If you have valid Exchange CALs for your users, you're able to use Entourage as a client. See this "how to buy" page for more details (but don't ask me where you're supposed to get the bits, because I don't know!)